This invention relates to electrostatographic reproducing apparatus and more particularly to a method and apparatus for reducing the contamination of the reproducing apparatus by charged toner particles escaping from a housing in which they are contained.
In the electrostatographic reproducing apparatus commonly in use today, a photoconductive insulating member is typically charged to a uniform potential and thereafter exposed to a light image of an original document to be reproduced. The exposure discharges the photoconductive insulating surface in exposed or background areas and creates an electrostatic latent image on the member which corresponds to the image areas contained within the original document. Subsequently, the electrostatic latent image on the photoconductive insulating surface is made visible by developing the image with a developing powder, referred to in the art as toner. Most development systems employ a developer material which comprises both charged carrier particles and charged toner particles which triboelectrically adhere to the carrier particles. During development, the toner particles are attracted from the carrier particles by the charge pattern of the image areas on the photoconductive insulating area to form a powder image on the photoconductive area. This iamge may subsequently be transferred to a support surface such as a copy paper to which it may be permanently affixed by heating or by the application of pressure. Following transfer of the toner image to the support surface, the photoconductive insulating surface is cleaned of residual toner to prepare it for the next imaging cycle.
One of the problems associated with electrostatographic reproducing apparatus is the contamination of the various processing stations by charged toner particles. This happens frequently as the charged toner particles may escape from the developer housing or the cleaner housing and float throughout the reproducing machine. These particles may be attracted to critical surfaces of the various processing stations, resulting in contamination and degradation of the performance of that subsystem. To maintain copy quality it is essential that the elements of the automatic reproducing machines remain substantially free from contaminating particles. One of the areas which is most sensitive to contamination is the optical system. If toner is allowed to collect on a lens or a mirror, for example, the total exposure is dramaticallly decreased and a problem with background may be created. Furthermore, if toner contamination is allowed with regard to the illuminating lamps, the lamp intensity goes down which also reduces the exposure. In addition, the same difficulty with regard to increased background may be had if toner is allowed to collect on the viewing platen. All these difficulties associated with toner collecting within the optical cavity provide for non-uniform exposure, increased background, and generally unacceptable copy quality, resulting in the need for unscheduled maintenance by a skilled technician. While the principal area that can be contaminated by loose, charged particles is the optical arrangement, it should be noted that such charged particles may interfer with other operations in an automatic reproducing machine. For example, if toner particles collect on the corona wires, streaking in the final copy can be created as a result of non-uniform charging.
Generally, the development system and the cleaning system have geometrical seals between the developer and the cleaner housing, and the photoconductive insulating member to prevent leakage of toner particles therefrom. In addition or alternatively thereto, the developer housing may be maintained at a negative pressure to insure that air flow is in an inwardly direction rather than an outwardly direction from the chamber storing carrier particles and toner particles. In these systems, typically a filter is used through which the air is pulled. With continued usage, the filter tends to clog up and the flow of air is reduced. Furthermore, such negative pressure devices are expensive and require additional space for the ducting within the automatic reproducing machine. In addition, it is generally observed that even with the foregoing precautions, toner particles tend to escape from within the developer housing. It has also been proposed to provide a toner material which contains a magnetic component for magnetic brush development system wherein the toner will be held onto the carrier, and thus not become airborne and go outside the developer housing and contaminate the machine.